In the field of graphic arts, image forming systems which can ensure very high contrast photographic characteristics (especially a gamma value (.gamma.) of at least 10) are required for satisfactory reproduction of continuous tone images or line originals in halftone images.
As an image forming system which can provide very high contrast photographic characteristics in the development with a processing solution having sufficient storage stability, the image forming systems in which a surface latent image type silver halide photographic material containing a specified acylhydrazine compound as a nucleating agent is developed with a processing solution which contains 0.15 mol/l or more of a sulfite preservative and is adjusted to pH 11.0-12.3 to form a very high contrast negative image having .gamma. of 10 or more have been proposed, such as disclosed in U.S. Pat. Nos. 4,166,742, 4,168,977, 4,221,857, 4,224,401, 4,243,739, 4,272,606 and 4,311,781.
In recent years, various ways to enable hydrazine compounds to produce their sensitizing and contrast-increasing effects by using a developer having a low pH value to stand long-range storage and long use have been proposed. For instance, the methods disclosed in JP-A-1-179939 and JP-A-1-179940 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") comprise using a photosensitive material which contains both a nucleation development accelerator having an adsorption group to silver halide emulsion grains and a nucleating agent having the similar adsorption group, and processing the photosensitive material with a developer adjusted to a pH value lower than 11.0, thereby forming very high contrast images. On the other hand, the use of highly active hydrazine compounds as a nucleating agent is disclosed in U.S. Pat. Nos. 4,998,604, 4,994,365 and 4,975,354, JP-A-3-259240 and JP-A-5-45761.
On the other hand, in preparing a silver halide photographic material, it frequently happens that a coating solution containing an emulsion and all the ingredients to be admixed therewith in a dissolved condition is allowed to stand for several hours prior to the application to a support. Under such a situation, the photographic material encounters a problem such that the highly active nucleating agent contained therein causes a considerable increase in intrinsic sensitivity of the emulsion or decomposes to such an extent as to exert bad influence upon photographic properties.
Thus, the technique of using highly active hydrazine compounds as a stable nucleating agent without spoiling their nucleation activity is still incomplete, and it has been expected to make improvements therein.